Re: Another round of scenic 997S photos
Quote:
mcdelaug said:Quote:
Jeannot said:
I thought variocam = two positions for camshaft and variocam + = linear ? is that not the difference vs. intake / exhaust?
Cheers
OK, I stopped being lazy and actually looked this up. Here's what I've learned.
Variocam, as originally implemented on the 968: a solenoid actuator would press against the timing chain to advance valve timing as engine RPM increased. Apparently there were three stages of advancement in the original Variocam.
Current products (987 for example) have a more sophisticated version of Variocam that relies on a rotary valve at the end of the camshaft to adjust valve timing (no more solenoid driven arm pressing against the timing chain).
Only the intake valves are modulated inthe current version of Variocam.
VariocamPlus: a more complex system of hydraulic tappets driven by a multilobe camshaft that can vary valve lift combined with Variocam's rotary valve system for adjusting valve timing. Only the intake valves are modulated in the current form of VariocamPlus.
So to summarize:
Variocam = timing
VariocamPlus = timing AND lift
Both only modulate the intake valves.
After having read about it, other manufacturers, including Honda and Toyota, appear to have created more sophisticated systems, although they are not used on all of their products.
See these links:
[url=http://www.autozine.org/technical_school/engine/vvt_31.htm]
[url=http://content3.us.porsche.com/prod/911/carrera4s_cabriolet.nsf/usaenglish/engine_transmissionvariocam_plus]
I hope this makes things a little more clear.
mcdelaug
Thanks for that
its just a little 50m stretch by the river 
